Desertification: Australia

OLYecology
251 - Earth's Tree News

Australia:

39) Major new research has found a direct link between land-clearing and climate change, and that land clearing triggers hotter droughts. Areas throughout southern Queensland cleared of native vegetation were found to have lost 12 percent of their summer rainfall and to have experienced an average 2C rise in temperatures. The study found that land clearing was just as significant in terms of climate change as greenhouse gas production from fossil fuels. Should these findings hold up and are found to be generalized throughout Australia and other areas globally clearing remaining natural vegetation, it would suggest a major revision in climate change policy-making is due. It is not enough to just focus upon greenhouse gas emissions, but maintaining natural vegetation through preservation, conservation and restoration may be an equally important policy response if global heating is to stopped. While reducing industrial emissions is critically important, we must also stop deforestation, which accounts for roughly 20 percent of all global emissions. Brazil's Amazon, for example, contains 70 billion tons of carbon, but activities such as cutting and burning make Brazil one of the largest carbon dioxide emitters in the world. http://inthegreen.typepad.com/blog/2007/11/protecting-fore.html

Australian scientists say they have found proof that cutting down
forests reduces rainfall.

The finding, independent of previous anecdotal evidence and computer
modelling, uses physics and chemistry to show how the climate changes
when forests are lost.

Ann Henderson-Sellers, director of environment at the Australian
Nuclear Science and Technology Organisation, at Lucas Heights, and Dr
Kendal McGuffie, from the University of Technology, Sydney, made the
discovery by analysing variations in the molecular structure of rain
along the Amazon River.

Not all water, Professor Henderson-Sellers said, was made from the
recipe of two atoms of "common" hydrogen and one of "regular" oxygen.

About one in every 500 water molecules had its second hydrogen atom
replaced by a heavier version called deuterium. And one in every 6500
molecules included a heavy version of the oxygen atom.

Knowing the ratio allowed scientists to trace the Amazon's water as
it flowed into the Atlantic, evaporated, blew back inland with the
trade winds to fall again as rain, and finally returned to the river.

"It's as if the water was tagged," she said.

While the heavier water molecules were slower to evaporate from
rivers and groundwater, they were readily given off by the leaves of
plants and trees, through transpiration.

"Transpiration pumps these heavy guys back into the atmosphere."

But the study showed that since the 1970s the ratio of the heavy
molecules found in rain over the Amazon and the Andes had declined
significantly.

The only possible explanation was that they were no longer being
returned to the atmosphere to fall again as rain because the
vegetation was disappearing. "With many trees now gone and the forest
degraded, the moisture that reaches the Andes has clearly lost the
heavy isotopes that used to be recycled so effectively," Professor
Henderson-Sellers said.

Tom Lyons, professor of environmental sciences at Perth's Murdoch
University, said there was now "certainly very strong evidence that
changes in surface conditions have an impact on the climate. In some
parts of the world the impact is very marked". The Amazon research
"helps us understand the mechanism".

Professor Henderson-Sellers said the average water molecule fell as
rain and re-evaporated fives times during its journey from the
tropical Atlantic to the river's starting point in the Andes
mountains. Forests played a vital role in keeping the heavy
molecules, and their far more common relatives, moving through the
water cycle.

"People will tell you that when you remove the forests it rains
less," she said, adding, however, such anecdotal evidence, and even
computer modelling, did not convince everyone.

"This is the first demonstration that deforestation has an observable
impact on rainfall."

Extensive clearing of native trees is making Australian droughts hotter and is an under-recognised factor in climate change, research shows.

The study by researchers from the University of Queensland and Queensland's Department of Natural Resources and Water shows that land clearing made the 2002-3 drought in eastern Australia 2°C hotter.

The research, published online in the journal Geophysical Research Letters, also found average summer rainfall has decreased by between 4-12% in eastern Australia and by 4-8% in southwest Western Australia because of land clearing.

These are historically the regions in Australia that have been most extensively cleared of native vegetation.

Dr Clive McAlpine, of the university's Centre for Remote Sensing and Spatial Information Science, says about 13% of the Australian continent has been cleared of native vegetation since European settlement in 1788.

However, in many agricultural areas in eastern Australia and southwest Western Australia more than 90% of native vegetation has been cleared.

"This study is showing Australian climate is sensitive to land clearing," he says.